Analysis of fluids (liquids and gases) in the petroleum industry provides identification of subterranean fluid characterization and variations in real time. Such analysis contributed to various useful finding, for example, to a determination that composition of hydrocarbons throughout the area of their distribution may be varied rather than homogeneous (caused by, for example, due to gravity, thermal gradients, biodegradation, water stripping, leaky seals, real time charging, multiple charging, and miscible sweep fluid injection, among other possible factors). The analysis is currently performed in a high-temperature environment in a so-called bore hole with the use of open-hole and cased-hole sampling tools that form a seal around a section of the borehole wall, or around casing perforations, while fluids in the formation are brought into the interior of the measurement tool.
Measurements effectuated with the use of Raman spectrometry (in which case a downhole measurement tool includes some type of a Raman spectrometer apparatus) rely on the strength irradiance of the Raman peak signal, often measured with the optical detector of the apparatus in a so-called back-scattering geometry, which is advantageous for production logging. Such peak strength or irradiance of the Raman-scattering optical signal, however, is subject to multiple variations during the measurement itself, caused not only by inhomogeneity of the target fluid chemical species and commingled flow of such species in the production well but also the power fluctuations of the laser light source used in the apparatus.
Such inhomogeneity of distribution of target chemicals and shortcomings of the measurements tool(s) begs a question of defining a reliable way to differentiate among the causes of variations in sought-after Raman measurement signal and appropriately correct or compensate for such variations to improve the quality, accuracy, and precision of the gas composition in the high-temperature environment of the borehole. This need remains unmet to-date in related industry.